Will a Pool Heat up Faster With the Cover On?

Most pool owners use a pool cover to keep water from evaporating and keep debris out of their pool. What they may not realize is that a pool cover can also help keep their pool warmer.

Pool cover manufacturers claim that having their cover over your pool can increase your water temperature by 10-15°F. Does a pool heat up faster with the cover on?

The answer is yes, pool covers can help your pool heat up faster, but the conditions need to be correct. Assuming you are only relying on the pool cover to heat your pool, then it would require around three consecutive days of warm, sunny weather to increase the water temperature that much. In other words, expect an increase in water temperature of 3-5°F for every 8-12 hours of sunlight that the pool gets with a pool cover on.

Keep reading on to learn how pool covers (both solid and liquid) can help your pool heat up faster, the pros and cons of using a solar pool cover, and how you can avoid the downsides.

How do pool covers heat your water?

Let’s be clear, it’s technically not the pool cover itself heating your water. Rather, a pool cover can create the conditions for your pool to retain heat and warm up. There are many ways it can do that, such as by:

Reducing evaporation

A pool cover can reduce water evaporation by as much as 95%. A majority of heat loss occurs due to evaporation, particularly at night when temperatures drop as well. When water evaporates, there is a cooling effect that will decrease the temperature around it.

This phenomenon can easily be experienced whenever we sweat; as the sweat evaporates, it cools our body down so we don’t overheat. When it comes to evaporation, wind and heat can cause water and chlorine to evaporate. However, with a pool cover on the wind is kept away from the pool so evaporation is drastically reduced.

In this way, you’re killing two birds with one stone. First, you don’t have to worry about refilling your pool as often. And second, you can help the pool water stay warmer.

Letting sunlight through

A regular pool cover is opaque, but solar pool covers are translucent and let light through. Thus, not only is the water being insulated against heat loss, but it is naturally getting warmed up by the sunlight.

However, unless you have another heat source, relying on just a solar pool cover and the sunlight to heat your pool can take multiple days.

In rainy and cloudy climates, this would be nearly impossible. In perpetually sunny and warm climates, this can be easily achieved. If you absolutely need your water to be warmer, buying a pool heater is the safer but expensive option, and having both is ideal.

Insulating the pool water

Not only does a pool cover keep water from evaporating during the day, but it also traps heat from escaping during the night. Solar pool covers often use air bubbles in their design. By keeping the air bubbles facing down, it acts as an effective insulator against heat loss, in the same way that a thermos can keep water warm.

That said, even regular pool covers have insulating benefits, but solar pool covers are even better at it.

Additional ways to heat your pool with a pool cover

Leave the pool pump on

One thing you may have noticed after taking the pool cover off is that the water along the surface is warmer, and the water below that is cold.

Not only does this feel uncomfortable to swim in, it can also lead to algae growth along the surface. You should run the pool pump so that it can circulate the water evenly, allowing for a more consistent water temperature instead.

Use a black solar cover

Black absorbs the most light whereas white reflects the most. If you want your pool cover to absorb the most light (heat), then get a black one.

It doesn’t have to stop there. Some pool owners install a black pool bottom solely because they want their pool to absorb more heat even with the pool cover off.

The difference in temperature between a black surface and literally any other color is substantial.

You can even test this by wearing a black T-shirt in the sun and then wear a white T-shirt afterwards. Or measure the temperature of a black car versus a white car.

Along this line of thinking, you should get a black pool cover to heat up your pool faster.

The black hose trick

Another cheap and effective solution to heat your pool water faster is the black hose trick. Buy a black hose and attach it to the outdoor water spigot. Leave the black hose coiled up in the sunlight so it can absorb the sunlight and heat up.

Then run water through it and the water that comes out will be warm. You can use this to refill your pool with warm water if your water is running low. Or you can just drape the black hose over the pool cover to heat up both simultaneously, or submerge an already heated up black hose underwater to transfer heat in that way.

Use a pool heater

By using a pool cover to aid a pool heater, you can drastically speed up how fast your pool warms up.

When heating up an uncovered pool with a pool heater, it is very inefficient because the exposed pool water is evaporating due to the wind.

Furthermore, if the temperature outside is also cold, then it’s doing your pool heater no favors. Give your pool heater a fighting chance by leaving it on with the pool cover on.

That way, water isn’t cooling down due to evaporation and cold air and much of the heat the pool heater generates will be retained.

Keep your expectations in check

As useful as pool covers are, keep in mind that they have their limitations.

First, understand that pool covers primarily insulate your pool; they do not generate any heat. As such, don’t expect pool covers to keep your pool warm in the dead of winter by themselves; you’d need a heater to do that.

Second, they are most effective with smaller pools. If you own a large and deep pool, then much of the water below the surface will be cold. The larger your pool, the more consecutive days of sunlight you need to increase the water temperature a noticeable amount, which quickly becomes infeasible if you are only relying on the pool cover to heat your pool.

Third, most people find it a hassle to take off the pool cover and then put it back on on a daily basis. That is perfectly understandable. Unless you have a reel system installed to make this process much easier, it can be annoying having to take off and put on the pool cover frequently.

Fourth, if you are not circulating the water, then the heat will primarily be trapped at the surface of the water. This feels unpleasant to swim in, but the higher temperatures can result in algae growth. Be prepared to use algaecide if you notice the pool water turning green along the surf